Ultrasound could waken a sleeping smart home

The home of the future, we are assured, will be swarming with tiny sensors: security cameras, carbon monoxide detectors, speakers and everything else. Few need to be running all the timebut how do you wake them up when theyre needed if theyre off in the first place? Ultrasound.

Thats the idea being pursued by Angad Rekhi and Amin Arbabian at Stanford, anyway. Their approach to the problem of devices that cant stay on, yet cant be all the way off, is to minimize the amount of energy necessary to send and receive a wake signal. That way the Internet of Things really only consumes power when theyre actively in use.

Radio, which of course all these tiny sensors use to transmit and receive information, is actually pretty expensive in terms of power and space. Keeping the antenna and signal processor ready and listening uses more energy than these devices have to spare if theyre to last for years on a charge.

Ultrasonic sensors, on the other hand, are incredibly power-efficient and require very little space. Ultrasoundsoundwaves above the human range of hearing, 22KHz or sois a much more physical phenomenon, and detecting it is easier in many ways than detecting radio frequency waves. Its a bit like the difference between a sensor thats sensitive to nearly intangible x-rays versus one that detects ordinary visible light.

Rekhi, a grad student in electrical engineering working under Arbabian, describes their approach in a paper just presented at the International Solid-State Circuits Conference in San Francisco. Its a simple idea in a waya small switch that hits a bigger switchbut the results are impressive.

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